The Real Heartworm Risk: Recognizing, Preventing and Treating a Life Threatening Problem - The Trupanion Blog
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The Real Heartworm Risk: Recognizing, Preventing and Treating a Life Threatening Problem


Heartworm is a real risk. Here are ways to prevent and treat this parasite.

Your veterinarian regularly sends heartworm prevention reminders for your dog or cat. At times, it can feel like it’s just another scare tactic for you to do more tests and spend more money. It’s not.

Heartworm occurs in every state, prevalent in some more than others. But here’s the thing, heartworm prevention is easier than treatment. Always.

This is a serious, potentially fatal disease spread by mosquitos. The parasite uses dogs, and in some cases cats, as host where adult worms colonize in the heart, lungs and blood vessels.

Veterinarians used both blood tests and X-rays to diagnose the disease. Blood work shows high levels of a specific white blood cell, eosinophils. X-rays show heart enlargement.

The Real Heartworm Risk

Recognizing Symptoms of Heartworm

Early stages of heartworm disease are not easy to diagnose. In fact, there may be no symptoms while the parasites are in juvenile stages. As the disease progresses, a mild persistent cough might develop and your pet might lose stamina.

Symptoms include respiratory issues, like wheezing and shortness of breath since heartworms affect lungs too. He might also cough or gag after eating or drinking. Other symptoms include vomiting, weight loss and overall lethargy in your pet.

Signs of advanced progression of the disease include pale gums, coffee-colored urine, a swollen belly and, eventually, heart failure.

Heartworm is only acquired from a host mosquito’s bite. Dogs don’t pass the parasites on to other dogs. However, mosquito presence increases heartworm risks among household pets.


Heartworm prevention is not treatment. What does that mean?

The reason your veterinarian requires testing if your dog has missed his heartworm prevention is that giving it can actually harm your pet, possibly fatally.

To most, that doesn’t make sense. If the heartworm prevention kills the parasite transferred from the mosquito, why wouldn’t it kill the other levels of the parasite?

It’s a reasonable question. First, the prevention medication doesn’t kill adult heartworms and offspring are released into the bloodstream. While the medication kills offspring, if they die in the bloodstream, a pet can go into shock and it can be fatal.

This is why it’s best to stay current on heartworm medication. Test your pet before starting heartworm prevention, have been off it for a while, or you are changing your medication.

Your veterinarian will advise on the best course of action.


Treatment is only for dogs. Cats are not typical hosts and adult heartworms generally don’t survive in cats. That being said, no treatment options exist for cats.

For dogs, early stages of the disease are treated with an injection into the back muscles. This targets juvenile worms that haven’t developed into adults. The treatment contains arsenic, which is why it can be so toxic to your dog.

Once adult heartworms develop, surgical removal is the only option, which is very dangerous and not always effective. A dog can host anywhere from one to 250 heartworms, with most cases having around 15. The worms look like spaghetti and can be anywhere from four to 12 inches long.

The parasite lives up to seven years in a dog, but only up to 4 in a cat.


Understanding these treatments makes it easy to see why the best treatment is prevention. This is why your veterinarian is so adamant about making sure your pet is protected against heartworm.

If you suspect heartworm, acting sooner than later is paramount to effectively treating the disease and giving your dog his best chance at recovery.

About the Author: Kimberlee is a versatile writer in print, digital and video content. Starting her career in 2001 in Los Angeles, she has recently returned to Hawaii to chase waterfalls and play in the water. Aside from writing, she runs, teaching pet first aid and CPR to help pet owners and rescues have more tools to keep pets safe and healthy.

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